The invention relates to an exhaust heat exchanger in particular for motor vehicles having an exhaust gas recirculation system (EGR), composed of a housing jacket for a coolant, and of a nest of pipes through which exhaust gas flows on the inside and around which coolant flows on the outside and which is held in the housing jacket by means of pipe plates, the nest of pipes, pipe plates and housing jacket forming an enclosed structure—such an exhaust heat exchanger has been disclosed by DE-A 199 07 163 by the applicant.
This known exhaust heat exchanger is an exhaust gas radiator such as is used in motor vehicles for recirculating exhaust gases in order to cool the hot exhaust gases. The exhaust gas radiator which is manufactured from stainless steel is essentially composed of a housing with a housing jacket through which a coolant flows, said coolant being removed from the coolant circuit of the internal combustion engine of the motor vehicle. A nest of pipes whose pipe ends are held by pipe plates which are themselves connected to the housing jacket is arranged in the housing jacket. The pipe ends are welded tightly to the pipe plates and the pipe plates are welded at the circumference to the housing jacket. In this respect the two pipe plates form, together with the housing jacket, what are referred to as fixed bearings. When this exhaust gas radiator operates, the pipes and housing jacket heat up to differing degrees because the exhaust gases flowing through the pipes have a higher temperature than the coolant flowing around the housing jacket. As a result, different degrees of expansion between the nest of pipes and the housing jacket occur, which leads to thermally induced stresses, i.e. compressive stresses in the pipes and tensile stresses in the housing jacket and flexural stresses in the pipe plates. The pipes of the nest of pipes, the pipe plates which hold the pipe ends, and the housing jacket thus form an enclosed structure in which the pipes are supported on the housing jacket by means of the pipe plates. In particular, in the case of exhaust gas coolers with a long length, such as are used in utility vehicles, the stresses which occur owing to the different degrees of expansion can lead to individual components failing or to the connection between the pipe plates being destroyed.
The object of the present invention is to reduce these thermally induced stresses, i.e. to decrease the resulting stresses in the components of the exhaust heat exchanger in order to achieve higher safety and a longer service life for the exhaust heat exchanger mentioned in the beginning.